Electrical device

ABSTRACT

An enclosure for an electrochemical device, especially useful for electrochemical cells having an internal pressure above ambient, wherein the enclosure is formed in accordance with techniques based upon aerosol container filling procedures.

This application is a division of application Ser. No. 728,672, filedOct. 1, 1976, now U.S. Pat. No. 4,052,537.

The present invention relates to electrical devices and to means andmethods for enclosing or containing electrical devices. Moreparticularly, the invention relates primarily to enclosures or housingsfor electrochemical cells, wherein said enclosure is formed similarly tocontainers of the type used for aerosol sprays. The invention isparticularly useful with electrochemical cells of the lithium/sulfurdioxide type which develop an internal pressure in excess of ambientpressures.

Electrochemical cells generally include two dissimilar electrodes in areactive medium enclosed within a housing, the housing comprising two ormore electrically conductive component parts electrically connected tothe electrodes but electrically isolated from each other, and thehousing providing external electrical termination for the cell. A commonconstruction for the housing for an electrochemical cell is a hollow,cylindrical, electrically conductive container having an open end and aclosure assembly adapted to seal the open end of the container. Theclosure assembly may comprise an electrically conductive, disc shapedclosure member and an electrically insulating gasket about the peripherythereof to electrically isolate the member from the container. Theclosure assembly is generally held in close engagement with thecontainer by an external edge of the container which is bent inwardly tophysically retard outward movement of the closure assembly, whereby tohold the closure assembly securely against the effect of increasedinternal pressure.

In the operation of an electrochemical cell, the housing should be andremain sufficiently hermetic so as to minimize leakage of the reactivemedium from the cell because leakage can cause damage to the cell itselfor to apparatus to be energized by the cell. In addition, the housingshould minimize the ingression of harmful contaminants from the ambientatmosphere which may cause deterioration of the electricalcharacteristics of the cell.

Cells having housings of the type described above, especially those ofthe lithium/SO₂ type have been difficult to fill and, when filled, oftendo not achieve the desired degree of hermeticity, especially when thecell is subjected to temperature cycling. The integrity of the sealbetween the container and the closure assembly has not been totallysatisfactory and has even led to the use of welding techniques and tothe use of expensive glass to metal seals in order to obtainhermeticity.

It is therefore a feature of the present invention to provide anelectrical device having a housing which minimizes the leakage ofmaterials from the interior of the device. Another feature is that thehousing for an electrical device of the present invention is relativelyeasy to manufacture using available equipment. Yet another feature ofthe present invention is that the housing for an electrical device isable to withstand temperature cycling without a significant loss inhermeticity.

These and various other features of this invention as well as manyspecific advantages will be more fully apparent from a detailedconsideration of the remainder of this disclosure including the appendedclaims in conjunction with the accompanying drawing in which:

FIG. 1 is a view of the component parts of an electrical device shown inpartial cross-section prior to closure of the housing; and

FIG. 2 is a partial cross-sectional view of the electrical device ofFIG. 1 after closure.

Generally, the present invention relates to a means and method forproviding an electrical device including a housing. The electricaldevice comprises an electrical body in a housing including an elongatedcylindrical container or can body having a height substantially greaterthan its diameter and an open end defined by a rim, the rim of thecontainer being rolled over, preferably inwardly of the wall of thecontainer, and a closure assembly or cover over and closing the open endof the container. The closure assembly includes a member having itsperiphery generally complementary to the shape of the rolled over rim ofthe container. The closure assembly is sealed to the rolled over rim ofthe container by crimping the closure radially outwardly or inwardly (orboth) to seal against said rolled over rim which providescounterpressure support for the crimping operation. In order to providetwo terminals of opposite polarity when, in the preferred embodiment,the electrical device is an electrochemical cell, an electricallyinsulating layer is positioned between the closure and the rolled rim.In a preferred embodiment, the electrical body of the cell includes alithium containing electrode and an SO₂ depolarizer and the containerand member consist essentially of aluminum, although other materialssuch as steel, etc. can of course be used.

A preferred embodiment of the invention is shown in FIGS. 1 and 2. InFIG. 1, the electrical device shown is an electrochemical cell 10comprising metallic container 12, closure assembly 14 and an electricalbody within the container. The electrical body 16 comprises convolutelywound anode and cathode electrodes 18 and 20 in an electrolyte (notshown). Positioned between adjacent turns of electrodes 18 and 20 areplastic separator strips 19 which are also convolutely wound. Inelectrical contact with the anode electrode 18 is anode currentcollector 21, the collector being shown in a nail type configurationwith a head 22 and a shank 23. Electrical contact is made from thecathode electrode 20 to the container 12 by a suitable connector (notshown). The entire rim 24 of container 12 is rolled inwardly to theshape of a torus to provide support for attachment and sealing ofclosure assembly 14. Note that, in the embodiment shown, rolled over rim24 of container 12 does not contact the side wall of the container.

Closure assembly 14 comprises electrically conductive member 26 andelectrically insulating material 28. Member 26 includes hollowprotuberance or cup 30 adapted to receive the end 22 of anode collector21 and includes lip portion 32 in a configuration that conformsgenerally to the shape of the rolled over rim 24 of container 12.Electrically insulating material 28 is disposed over the underside ofedge portion 32 so as to electrically isolate the member 26 fromcontainer 12 in the completed device.

FIG. 2 illustrates the completed closure of the electrochemical cell 10of FIG. 1. The hollow protuberance or cup 30 has been brought intoelectrical contact with anode current collector head 22 and theinsulating material 28 disposed on edge portion 32 is in engagement withrolled over rim 24 of the container 12. A suitable tool or tools (nowshown) have crimped member 26 inwardly beneath the lower edge of thehead portion 22 of anode collector 21 and radially outwardly beneath therolled over rim 24 of container 12 to form annulus 25 which extendsbeneath torus 24. Member 26, excluding shaped edge portions 32, now hasa diameter greater than the diameter of the inner portion of rolled overrim (torus) 24. Thus, closure assembly 14, including member 26, iseffectively held in close engagement with container 12 and therebyprovides a seal for the open end of the container.

Typically, the forming or crimping of member 26 about rolled over rim 24is accomplished by crimping or forming the member 26 to container 12 bywhat is known as an "expanding collet" type crimping machine of a typewhich is well known in the aerosol container art. Similarly, member 26is formed about anode collector head 22 by forming or crimping theprotuberance or cup 30 about the anode collector head 22 by a "pedestal"crimping machine having a contracting collet. This machine forms thewalls of protuberance or cup 30 under the nailhead portion of anodecollector head 22 to help provide good electrical contact between themember 26 and the anode collector. These steps can be carried outsimultaneously or in seriatim. To further insure good electricalcontact, it may be desirable to weld the anode collector 22 to themember 26 by any suitable method such as by parallel electroderesistance welding.

As can be seen from FIG. 2, the crimping of member 26 into theconfiguration shown causes member 26 to have a larger diameter insidethe container 12 than the diameter of the innermost periphery of torus24. With such a construction, closure assembly 14 is not likely todisengage if internal pressures are generated by the electrical body 16.In addition, because rim 24 is not completely rolled over to engage thewall of container 12, excess crimping forces on member 26 can betolerated due to the slight resiliency of the rolled over rim. Anyincrease in internal pressure also acts to decrease leakage due to theincrease in the pressure of annulus 25 against torus 24.

In a preferred embodiment of the present device the container 12 ispreferably an aluminum can into which the electrochemical elements areplaced and a small punch press thereafter curls the can lip to formtorus 24. The torus will have a ring shaped cross section of about 0.13inch in diameter which gives the torus itself about a one inch insidediameter opening based upon the diameter of the can body which has anoutside diameter of about 1.25 inches. The use of this size can and curlis extremely advantageous because it conforms to the aerosol industrystandard and closely approximates the standard D cell diameter. Thismakes it possible to utilize ordinary aerosol industry filling andsealing technology to produce the cells of the invention. Suchtechnology as used in the aerosol industry has been highly developedwhereby the cells can be filled with a pressurized, normally gaseouselectrolyte which is analogous to the Freons or other volatilepropellants which are in common use in the aerosol industry.

A preferred filling method that has been adapted from the aerosolindustry involves placing the open ended can, having torus 24 thereonand complete with electrochemical elements therein, under anevacuation-electrolyte fill head. The gas is evacuated from the can andreplaced with a metered amount of electrolyte which in this instance isSO₂ that has been chilled to a temperature sufficient to maintain it asa non-volatile liquid. Normally a temperature in the range of -17 to-35° C. will be adequate. While the boiling point of the electrolyte isapproximately -10° C. the use of a substantially lower temperature asset forth above is highly desirable so that the mass of chilledelectrolyte will be adequate, when introduced into the can 12, toimmediately chill the can and contents below the boiling point of theelectrolyte and to maintain the entire article below that point for atleast about 30 seconds during which time cap 26 can be placed on saidcontainer 12 and crimped into sealing relation in the manner indicatedabove. Thereafter, one or more layers 35, 37 (FIG. 2) of insulatingplastic material can be placed around the cylindrical side wall of canbody 12 to extend from the closure to the bottom of said can body.Advantageously such layers will be formed by heat shrinking one or moretubes of shrinkable plastic around said can body in a manner known inthe art.

An alternate method which is useful for filling the electrical devicesof this invention involves the evacuation of the can and the pressurefilling of electrolyte at room temperature. In this embodiment of theinvention the closure 14 is loosely placed on can body 10 having theelectrochemical elements previously placed therein and having torus 24previously formed thereon. The loosely covered can is placed under afilling head, the filling head seals the upper end of the can from theexternal environment, and a vacuum is drawn whereupon the air is removedfrom the container. Thereafter, electrolyte under pressure is filledinto the can body through the space between the can and the looselyfitting closure. The closure thereafter is forced onto the upper edge ofthe can body and crimped into sealing relationship with the torus.Thereafter, one or more layers of insulating material may be placedaround the side wall of the can body.

Member 26 is analogous to the valve mounting cup commonly used in theaersol industry but in view of the elimination of the valve means,member 26 is referred to as a blind mounting cup. Thus, in accordancewith this invention, the highly developed technology of the aersolindustry has been adapted to the non-analogous field of batterieswhereby it has been made possible to form batteries in an inexpensivemanner utilizing existing equipment and known from the non-analogousaerosol field thereby eliminating the necessity of developing specialmachinery to achieve results which were apparently unobtainable in thebattery field except by the provision of expensive technology andhermetic sealing methods and equipment.

Although the device shown in FIGS. 1 and 2 is an electrochemical cell,it should be realized that the housing could be adapted to enclose otherelectrical devices such as electrolytic capacitors. Preferably container12 is a unitary structure although the container could be made from anassembly of more than one component. Suitable electrically conductivematerials for the container include steel, aluminum, copper, silver,alloys thereof and the like, aluminum being preferred for someelectrochemical cell applications.

In the same fashion, member 26 may be a unitary structure or a compositeof different structures. Suitable electrically conductive materials forthe member also include steel, aluminum, copper, silver, alloys thereofand the like, steel is preferred for Li/SO₂ electrochemical cellapplications. For certain applications, it may be desirable for themember to contain both electrically conductive portions and electricallyinsulative portions. By selecting appropriate materials for thecontainer 12 and members 22 and 26, the device 10 can be madesubstantially non-magnetic and thereby useful in systems for detectingmagnetic items.

In the embodiment shown in FIGS. 1 and 2, electrically insulatingmaterial 28 is disposed between edge portion 32 of the closure member 26and the rolled rim 24 of the container 12 to electrically isolate theseportions of the device 10. Such insulating material 28 is necessary whenthe member 26 is entirely electrically conductive. However, if member 26is a composite of electrically conductive portions and electricallyinsulating portions, insulating material, 28 disposed between the member26 and the rolled rim 24 may not be necessary.

In those preferred embodiments where electrically insulating material 28is used, it may take several different forms. A preformed gasket orgrommet of a suitable inert polymeric material such as is disclosed inapplication Ser. No. filed on even date herewith, which is apolyhalogenated hydrocarbon resin may be utilized. Alternatively, aprepolymer or polymer resin material may be applied to either the edgeportion 32 of member 26 or to the rolled rim 24 of container 12 or toboth and then flowed and/or cured by methods such as the application ofheat after closure of the device 10. Suitable insulating, polymeric,inert materials for a preformed gasket or for applied resin materialinclude polytetrafluoroethylene, neoprene, polyurethane, polypropylene,polyethylene, and the like. Heat shrinkable resin sleeves may also beapplied to the rim 24 of container 12 prior to or after rolling of therim.

Materials that will adhere to the rolled over rim 24 and the member 26are preferred for use as element 28. Suitable materials of this typeinclude polymeric, polyhalogenated hydrocarbon materials such as: FEPcopolymers which are copolymers of fluorinated ethylene and propylene;PVF₂ which is a homopolymer of vinylidene fluoride; ETFE copolymerswhich are copolymers of ethylene and tetrafluoroethylene; CTFE polymerswhich are chlorotrifluoroethylene resins and E-CTFE copolymers which arecopolymers of poly (ethylene-chlorotrifluoroethylene); and polymershaving a fluorocarbon backbone and perfluoro alkoxy (PFA) side chainswherein the alkoxy radical contains from 1-6 carbon atoms.

While the present invention is particularly useful for electrochemicalcells in which the anode 18 is preferably lithium metal, other activemetals above hydrogen in the activity scale or electromotive seriesincluding sodium, potassium, rubidium, calcium, magnesium, strontium,barium and cesium may be used either singly or in combination. Similarlythe cathode current collector 20 on which the solvent or co-solvents areelectrochemically reduced will advantageously be a screen, havingapplied thereto a mixture of an inert and electrically conductivematerial such as carbon black, graphite, or other electrical conductorsof high surface area, and, preferably, including absorbing and bindingagenst. Normally gaseous electrolytes for which the cells of the presentinvention are particularly useful include such materials as sulfurdioxide (SO₂), nitryl chloride (NO₂ Cl), nitrosyl chloride (NOCl), andnitrogen dioxide (NO₂).

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that the structureand method defined herein will be useful for the formation of otherelectrical devices such as, for example, electrochemical cells havingother fluid electrolytes. In addition, numerous other modifications maybe made by those skilled in the art without actually departing from thespirit and scope of the invention as defined in the appended claims.

I claim:
 1. A method for forming a pressurized electrical devicecomprising the steps of loosely placing a closure on a can body havingelectrical elements therein and having a torus formed thereon byinwardly rolling the rim of the upper end of the can, sealing the areasurrounding the upper end of the can and closure from the externalenvironment, removing the air from the container and from the areasurrounding the upper end of the can and closure, filling electrolyteunder pressure into the can body through the space between the can andthe loosely fitting closure, and thereafter forcing the closure onto theupper edge of the can body and crimping it into sealing relationshipwith the torus.
 2. A method of forming a pressurized electrochemicalcell comprising the steps of: curling the rim of the open upper end of acylindrical metallic can body to form a torus the innermost portion ofwhich has a diameter less than the diameter of said can body;positioning an anode and a cathode within said can body, electricallyconnecting one of said anode or cathode to said can body and the otherto a cover for said can body, evacuating the gas from said can body,cooling a normally gaseous electrolyte to a temperature below itsliquefaction point and introducing the thereby liquefied electrolyteinto said can body, immediately closing said can body with said coverand crimping said cover against said torus to close said electrochemicalcell.
 3. The method as in claim 2 wherein an insulating polymericmaterial is placed between said can body and said cover todielectrically separate said cover and said can body.
 4. The method ofclaim 2 wherein said electrolyte is cooled to a temperature sufficientlybelow its liquefaction point to enable the mass of electrolyte to coolthe can body and its contents below said point.
 5. The method of claim 4wherein said temperature is below -17° C.
 6. The method as in claim 5wherein said electrolyte is sulfur dioxide (SO₂).
 7. The method as inclaim 6 wherein said anode is lithium.
 8. The method of claim 2 whereinsaid cover is placed on said can within about 30 seconds after saidelectrolyte is added.